The present invention relates in general to alarming and more particularly concerns an improvement of the invention of Monte G. Seifers disclosed in U.S. Pat. No. 4,136,334 granted Jan. 23, 1979, for TIMED ALARMING USING LOGICAL INVERTERS. This improvement selectively provides a continuous or pulsed alarm signal and includes means for preventing damage to relatively low voltage capacitors by high voltage transients caused by inductive load dump in the vehicle in which the alarm is installed.
The aforesaid patent discloses improved apparatus for interdependent timing mechanisms that create a triggered before disarmed alarm system with automatic reset that dissipates negligible power in the rest condition. The alarm signal there provided is a continuous alarm that restricts the time in which a horn or other warming device operated by the vehicle battery may sound the alarm condition. Yet, the provision of a continuous alarm signal may be desirable, for example, when the audible signal is provided by an electronic siren. A problem with the prior art alarm circuit was that occasionally capacitors became defective after installation. It was discovered that the cause of this problem was inductive load dump producing a high voltage transient when a battery cable was connected or disconnected.
Accordingly, it is an important object of this invention to provide an improvement of the aforesaid patented invention.
It is a further object of the invention to achieve the preceding object while allowing the selection of either continuous or pulsed alarm signals.
It is a further object of the invention to achieve one or more of the preceding objects while preventing low voltage capacitors from being damaged by high voltage transients caused by inductive load dumping.